Alkali metal ferrates



United States atent ALKALI METAL FERRATES John Ruiford Harrison, Niagara Falls, and Richard C. Toole, Grand Island, N. Y., assignors to E. I. du Pont de Nemours and Company, Wilmington, DcL, a corporation of Delaware No Drawing. Application May 31, 1955 Serial No. 512,296

Claims. (CI. 23-50) This invention relates to novel ferrates of the alkali metals, to their preparation and to some of their uses.

Heretofore, a few compounds have been reported in which iron exhibits a valence of four. Thus, Scholder, Angew. Chem, 66, 461-467 (1954), discloses BaFeO This compound is relatively inert towards water and, so far as known, possesses no uses.

It has now been discovered that the corresponding ferrates of the alkali metals can be prepared, though by methods differing from those of Scholder, and that the compounds are soluble in and reactive towards water. The reaction with water yields the known ferrates in which iron has a valence of six. The novel alkali metal ferrates thus provide a simple route to the normal ferrates, useful oxidizing agents.

Since this specification considers several different valences of iron, one at least of which is unusual, conventional nomenclature is generally dispensed with herein. Instead the Stock System, recommended by the International Union of Chemistry, is adopted. This system is discussed, for example, in the J. Am. Chem. Soc. 63, 889 (1941). I. U. C. terminology, including that for pentavalent iron no further mentioned, is listed in the following table:

Some objects of the invention may accordingly be listed as follows:

(1) To provide new and useful compositions of matter;

(2) To provide new alkali metal ferrates;

(3) To provide alkali metal ferrates in which iron has a valence of four;

(4) To provide a method for synthesizing an alkali metal ferrate(IV); and

(5) To provide a novel method for making a ferrate- (VI). Additional objects will be evident hereinafter.

The first four 'of the above-mentioned objects are achieved in accordance with this invention by a process of reacting the ferrate(III) of an alkali metal with the oxide of the same, or a different, alkali metal to yield the corresponding ferrate(IV). The ferrateflll) used as a starting material may, alternatively, be replaced by its progenitors, as, for example, a carbonate andferric oxide. Either the oxide or the peroxide may be selected for reaction with the ferrate(lII), but the preferred choice depends to some extent on metal involved. I t

the particular alkali best results with the monoxide.

The reaction producing the ferrate(HI) is well known and may be represented by the equation:

(a) Heat XzCOa F6203 2XFeO2 T002 where X is an alkali metal such as potassium or sodium. The reaction yielding the ferrate(IV) may then be expressed, in theory, by the equation:

where Y also stands for an alkali metal, the same as or different from that represented by X.

Reaction b is accomplished by comminuting and intimately mixing the solid reagents in sequential or simul-' taneous steps and then heating the mixture. In some cases it is found desirable to preheat the mixture in an inert atmosphere under controlled conditions. The preheating serves to increase the yield when certain reactants are employed. No reaction occurs in the absence of free oxygen although the latter does not appear in the theoretical equation.

Compounds of the type XYFeO such as Na Fe0 or KNaFeO are black crystalline substances which dissolve readily in water to give the familiar red coloration of ferrate(VI). An equation for the dissolution of the sodium compound can be written as:

A major utility of the ferrates(IV) is thus the preparation of the ferrates(VI), known oxidizing agents. The solutions can be used directly as oxidants if it is so desired.

In practice an excess of iron oxide or ferrate(III) does not interfere with the yield of ferrate(VI). The fifth object of the invention disclosed above can, therefore, be simply accomplished by adding the product of the reaction between ferrate(III) and peroxide to water without separating the ferrate(IV). Since peroxide destroys some of the ferrate(VI), it should be held to a minimum in the product to be dissolved. Some peroxide is, however, almost always found in the ferrate(IV) even when an alkali metal monoxide and an oxygen-containing gas are employed as starting materials.

The most important variables encountered in producing ferrate(IV) by the process described are the reactants, the reaction temperature, the contact time, the mole ratio of the reactants and the pressure of the gas utilized. When a pretreatment of the reactants is employed the conditions therefor are also important.

The choice of alkali metal for use in Reaction b, the

central feature of the invention, is, of course, optional and determined by the product desired. A slight difference, however, appears in the reactivity of sodium and potassium ferrites. When sodium ferrite is utilized, the best yields are obtained with the peroxide as the other reactant. Potassium ferrite, on the other hand, gives the While the reaction has been practiced only with sodium oxides, the more expensive potassium compounds can probably be substituted for these if it is so desired. The formation of interfering superoxide is, however, more diflicult to suppress with potassium than with sodium.

As noted above, free oxygen is necessary for the reaction to proceed with either the monoxide or the peroxide.

The role of theoxygen when the monoxide is a reactant can readily be explained, since it enters directly into the reaction. When the peroxide is used, oxygen probably acts as a catalyst. Almost any gas which contains free oxygen and is otherwise compatible with the reactants can be used as a source of oxygen. Purified air, for example, is perfectly satisfactory. Oxygen gas is another source. Artificial atmospheres inert except for the oxygen contained can also be employed but are unnecessarily expensive.

In addition to, or in substitution for, the oxide or peroxideof sodium, compounds which generate the oxide on heating may be used as reactants. Such compounds include sodium carbonate, bicarbonate, nitrate, nitrite and the like. It will be understood that evolved gases should be removed from the reactant mixture as fast as possible in each case. The presence of free oxygen is necessary with these substitutes as with the peroxide or monoxide.

At atmospheric pressure, the preferred temperature range for Reaction b is about 300-500 C. Reaction does not occur below 275 C. and remains slow up to about 300 C. Decomposition of the ferrate(IV) begins at about 500 C. Generally a temperature of above about 400 C. is unnecessary but the range 400500 C. can be used.

At atmospheric pressure, a temperature of 300-500 C. and with preferred quantities of reactants, formation of the ferrate(IV) is virtually completel in /2l hour. If an excess of peroxide is used to increase the yield, it is generally necessary to'destroy this excess to preserve the ferrate(VI) formed in aqueous solution. Periods much longer than 1 hour are required to eliminate the excess, around 1624 hours being necessary for best results.

The peroxide:ferrate(lII) mole ratio has a marked effect on the yield of ferrate(IV). When sodium compounds alone are employed, the preferred ratio is around 2:1, both higher and lower ratios giving reduced yields.

In general, yields are much better at ratios between 1:1 and 3:1 than at lower values and somewhat better than at higher values. The effect of changes in monoxidezferrate(III) ratios is about the same where monoxide is used as it is where peroxide is used. Best yields are obtained at an oxide:ferrate(lIl) ratio of about 1:2 when potassium ferrite is substituted for its sodium analogue.

It might be expected that, at increased oxygen pressures, a purer ferrate(IV) would be formed. Unless special precautions are taken as noted below, increased purity is, however, not found. No effect at all is observed on sodium peroxide:ferrate(III) mixtures when the pressure of pure oxygen is increased from one atmosphere to 1000 p. s. i. As the oxygen pressure passes 1000 p. s. i. a superoxide, NaO being representative, is formed. The superoxides do .not react as the peroxides and decrease the yield of ferrate(IV). Pressures greater than about one atmosphere cannot be used'with potassium compounds because of the formation of the superoxide.

The formation of sodium superoxide is avoided by subjecting the intimately mixed reactants, i. e., sodium ferrate(III) and a sodium oxide, to a pretreatment. This pretreatment consists in heating the reactants to a high temperature, around 550-650 C. with 600 C. being preferred, in nitrogen or a truly inert gas such as neon, helium, argon or the like. An ill-defined mixture of compounds is thus formed which contains no free oxide of sodium and cannot be oxidized to superoxide. The mixture can, nevertheless, be oxidized to ferrate(IV) at about 1000-3500 p. s. i. with a higher yield than is obtained at atmospheric pressure. Either air or oxygen under pressure is a convenient source of oxygen under these conditions.

From the principles of the foregoing paragraphs, the preferred embodiments of the invention are apparent. For

the preparation of sodium ferrate(IV), sodium peroxide,

The best yield of sodium ferrate(IV) and 96% in 5 days.

has been obtained with a 1:1 mixture of Na O and NaFeO heated at 600 C. in nitrogen for several hours and then oxidized at 350 C. in pure oxygen at 3000 p. s. i. for 4 hours.

The preferred embodiment for producing KNaFeO is in general similar to that for preparing Na FeO at atmospheric pressure but differs somewhat in details. Thus, the preferred ratio of KFeO :Na O is between about 1:1 and 2:1. Almost conversion of ferrate(III) to ferrate(IV) can be obtained by heating a mixture of KFeO and Na O having a mole ratio of 2:1 at 300-450 C. in air under atmospheric pressure for several hours. This conversion, higher than any obtained with sodium compounds alone, is obtained without increaed pressure or pretreatment of the reactants.

There follow some examples which illustrate the invention in more detail. In these examples all percentages are by weight.

Example 1 A series of preparations was made in carbon dioxidefree air at atmospheric pressure by heating comminuted and intimately mixed sodium peroxidc and preformed so dium ferrate(III) at 400 C. In each case the product, containing NaFeO gave the characteristic red color of ferrate(VI) when dissolved in water. In /zl hour a mixture having initially a Na o zNaFeo mole ratio of 1:2 contained about 26% of ferrate(IV). 72% of the desired product was formed at a mole ratio of 4:2 and 61% at a mole ratio of 6:2. A sample with a 3:2 Na o zNaFeo mole ratio gave 543% ferrate(IV) after /2 hour and 57.5% after 16 hours. The corresponding figures for peroxide in the product are 19.0% and 2.8%.

Example 2 An intimate mixture of sodium monoxide and sodium ferrate(III) with a mole ratio of 1:2 was heated at 400 C. for 2 hours. The weight of ferrate(IV) in the product was 20%. A similar run using sodium peroxide showed 26% of ferrate (IV) in the product.

Example 3 An intimate mixture of sodium oxide and ferrate([ll of a mole ratio of 1:2 was heated at 400 C. in dry nitrogen at atmospheric pressure for 19 hours. It was then heated at 350 C. for four hours under 3100 p. s. i. of oxygen. The product contained 55.2% of ferrate(IV) and substantially no peroxide or superoxide. The yield was increased to 72.3% by preheating an identical mixture in nitrogen at 600 C. and then heating it under oxygen. A 1:1 mixture gave a product containing 83.7% ferrate(IV) when preheated in nitrogen at 600 C. and then heated under 3100 p. s. i. of oxygen at 350 C.

Example 4 A 2:1 molar mixture of sodium carbonate and ferric oxide was heated at 1100 C. for 16 hours in nitrogen. The preheated mixture was then heated at 400 C. in oxygen at 1 atmosphere for one hour. A 9.4% content of ferrate(IV) was found in the product. In a repetition of this experiment, using, however, oxygen at 2000 p. s. i. in the final step, 166% ferrate(IV) was obtained.

Example 5 Intimate mixtures of KFeOg and Na o having a mole ratio of 2:1 were heated at various temperatures "in carbon dioxide free air 'at atmospheric pressure. At 350 C. the product was found to comprise 86% KNaFeo At 450 C. and also at 300 C. the product contained 725%C of the ferrate(IV). No reaction occurred at 1 Other mixtures having KFeo zNa O mole ratios of 2:1 showed 89% of ferrate(IV) in the product after 16 hours The 96% figure represents almost 100% conversion of ferrate(III) to ferrate(IV).

Having described our invention, we claim:

1. The method of preparing the ferrate (IV) of an alkali metal of the group consisting of sodium and ptassium which comprises heating to a temperature of at least about 275 C. the ferrate (III) of an alkali metal of said group admixed with a member of the group consisting of the monoxide, peroxide, carbonate, bicarbonate, nitrate and nitrite of an alkali metal of the aforesaid group in the presence of gaseous oxygen.

2. The method of preparing disodium ferrate (IV) which comprises heating sodium ferrate (III) at a temperature of about 300-500 C. with a member of the group consisting of monoxide, peroxide, carbonate, bicarbonate, nitrate and nitrite of sodium in the presence of gaseous oxygen.

3. The method of preparing disodium ferrate (IV) which comprises heating an admixture of sodium peroxide and sodium ferrate (III) with a Na O :NaFeO mole ratio of between about 1:1 and 3:1 at a temperature of about 300-500 C. in the presence of gaseous oxygen.

4. The method of claim 3 in which the heating is carried out for between about V2 and 16 hours.

5. The method of preparing disodium ferrate (IV) which comprises heating an admixture of sodium monoxide and sodium ferrate (III) with a Na OsNaFeO mole ratio of between about 1:1 and 3:1 at a temperature of about 300-500 C. in an atmosphere containing gaseous oxygen.

6. The method of claim 5 in which the admixture is preheated at around 550-650 C. in an inert gas for about 1-4 hours before heating in the oxygen-containing atmosphere.

7. The method of claim 6 in which the atmosphere is substantially pure oxygen supplied at a pressure of 1,000- 3,500 p. s. i.

8. The method of preparing disotiium ferrate (IV) which comprises heating an intimate mixture of sodium monoxide and sodium ferrat; (III) with a mole ratio of about 1:1 in nitrogen at atmospheric pressure for 2-4 hours and sequentially heating said mixture at about 600 C. for about 4 hours in oxygen at a pressure about 3,000 p. s. i.

9. The method of preparing potassium sodium ferrate(IV) which comprises heating an intimate mixture of potassium ferrate (III) and sodium oxide with a KFeO :Na O mole ratio of between about 1:1 and 2:1 at a temperature of about 300-500" C. maintained for about /z-16 hours in the presence of gaseous oxygen.

10. The method of preparing the ferrate (VI) of an alkali metal of the group consisting of sodium and potassium which comprises dissolving in water the reaction mixture obtained by heating the ferrate (III) of the metal at a temperature of at least 275 C. with a member of the group consisting of the monoxide, peroxide, carbonate, bicarbonate, nitrate and nitrite of an alkali metal of the group consisting of sodium and potassium in the presence of gaseous oxygen.

References Cited in the file of this patent UNITED STATES PATENTS Krassa Aug. 15, 1933 OTHER REFERENCES UNITED STATES PATENT OFFICE CERTIFICATE OF (IORRECTION Patent No 2,835,553

May 20 1958 John Rufford Harrison et al.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 24, for "NaFeO3" read Na2FeO3 Signed and sealed this 8th day of July 1958.,

(SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Commissioner of Patents Attcsting Oificer- 

1. THE METHOD OF PREPARING THE FERRATE (IV) OF AN ALKALI METAL OF THE GROUP CONSISTING OF SODIUM AND POTASSIUM WHICH COMPRISES HEATING TO A TEMPERATURE OF AT LEAST ABOUT 275*C. THE FERRATE (III) OF AN ALKALI METAL OF SAID GROUP ADMIXED WITH A MEMBER OF THE GROUP CONSISTING OF THE MONOXIDE, PEROXIDE, CARBONATE, BICARBONATE, NITRATE AND NITRITE OF AN ALKALI METAL OF THE AFORESAID GROUP IN THE PRESENCE OF GASEOUS OXYGEN.
 10. THE METHOD OF PREPARING THE FERRATE (VI) OF AN ALKALI METAL OF THE GROUP CONSISTING OF SODIUM AND POTASSIUM WHICH COMPRISES DISSOLVING IN WATER THE REACTION MIXTURE OBTAINED BY HEATING THE FERRATE (III) OF THE METAL AT A TEMPERATURE OF AT LEAST 275*C. WITH A MEMBER OF THE GROUP CONSISTING OF THE MONOXIDE, PEROXIDE, CARBONATE, BICARBONATE, NITRATE AND NITRITE OF AN ALKALI METAL OF THE GROUP CONSISTING OF SODIUM AND POTASSIUM IN THE PRESENCE OF GASEOUS OXYGEN. 